Winch with hydraulic motor especially for helicopter equipped with sonar

ABSTRACT

A winch operates with a hydraulic motor which is supplied by a servo-valve. The servo-valve is connected as a 3-way system so that the supply hose used as a discharge when the load is being winched up is connected directly to the fluid return and so that during the descent, this motor is no longer supplied with high pressure and the fluid is circulated in a closed circuit without pressure. Fluid is refreshed with a flow rate low enough so that it does not excessively increase the supply of energy, but high enough that it limits the overheating of the fluid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to winches which are moved by a hydraulicmotor. It applies more particularly to winches equipping helicopters andwhich especially allow there to be immersed in the sea a sonar known asa "dipping sonar" which is suspended from the end of the cable of thewinch so that it can be brought back on board the helicopter afterwards.

2. Discussion of the Background

Helicopters are often equipped with a winch which allows loads to be setdown and picked back up in places which are difficult to access, bymaking the helicopter hover.

In the case of helicopters specialized for submarine hunting, use ismade of a very specific winch which, with the aid of an electricsupporting cable, allows a specialized sonar to be immersed fordetecting the presence of a submarine, and allows this sonar to berecovered in order to go and take measurements a little further on.

Such a mission imposes particularly severe stresses on the deviceemployed. Indeed it is necessary to be able to lower and to raise thesonar with a high average speed, typically 5 m per second, whileprotecting the cable which is relatively fragile in order to avoid lossof the sonar. Furthermore, it is also necessary to ensure the safety ofthe helicopter by avoiding sharp and excessive forces at the winch byavoiding the overheating of the oil of the hydraulic circuit, becausethe volume of hydraulic fluid is low for reasons of weight and there istherefore the risk of its temperature rising rapidly and exceeding thesafety temperatures. These constraints have to be respected while at thesame time maintaining good reliability and nevertheless keeping down thecost of the device.

Winches are known which are designed so that descent takes place by freefall by mechanically disengaging the motor from the drum on which thecable is wound. This method is clearly dangerous.

The winches most commonly used at the present time include a hydraulicmotor which both allows the sonar to be raised back up and allows itsdescent to be controlled. Such a winch assembly has been representeddiagrammatically in FIG. 1.

In this winch, a hydraulic motor 101 drives a worm 102 which itselfdrives a wheel 103 keyed to the shaft 111 of the drum on which the cableis wound and unwound. This worm system makes it possible in a simple andreliable manner to obtain the desired reduction ratio. It does, however,have the drawback of having a low efficiency, some 40%, in the reversedirection. In this mode of operation, that is to say when the load onthe cable is driving the hydraulic motor when this load is descending,this low efficiency here is of little inconvenience bearing in mind thecontrol circuits used, represented diagrammatically by the hydrauliccontrol unit 104.

Furthermore, use is made of a brake 105 actuated by the hydraulic energyof the unit 104 or with the aid of a control lever 106. This brakeallows the winch to be immobilized in periods when it is not operating.

Finally, in order for it to be possible for the winch to be operatedeven if the hydraulic system breaks down, an electric motor 107 isprovided which drives the worm 102 by means of a reduction gear 108 anda dog clutch 109. This dog clutch is engaged mechanically by a secondcontrol lever 110 which furthermore mechanically controls a dischargevalve situated in the hydraulic unit 104, which allows the hydraulicmotor 101 to rotate freely in such cases.

FIG. 2 represents the mechanical part of FIG. 1, simplified, and thehydraulic unit 104 in greater detail.

The load 201 on the winch is fastened to the end of a cable 202 which iswound on a drum 203. This drum 203 is driven by the hydraulic motor 101itself released, or immobilized, as the case may be, by a brake 105.

The motor 101 is fed from a source of hydraulic fluid under pressure Pby means of a shut-off valve 204 and of a 4-way servo-valve 205. Theshut-off valve makes it possible to apply all of the pressure to theservo-valve under the control of a pilot electro-valve 206. The latter,on the basis of a low-power electric control signal C1, applies acontrol pressure to the shut-off valve 204 which releases the mainpressure. Upon stopping, the control fluid for the valve passes backthrough the pilot electro-valve to return to the fluid reservoir 207 viaa return R. This reservoir has been represented with the appearance ofan open tank, but this representation is purely symbolic and it is infact the main hydraulic-fluid reservoir of the helicopter, from whichthis fluid is repressurized and sent back to the inlet P.

The servo-valve 205 is of the known 4-way type, controlledproportionally under the effect of a low-power electric control signalC2. This servo-valve makes it possible, on the one hand, to reverse thedirection of flow of the hydraulic fluid between, on the one hand,circuits P and R and, on the other hand, the two hoses for supply anddischarge of the motor, and, on the other hand, to regulate preciselythe quantity of hydraulic fluid allowed into the motor and therefore thesupply pressure thereof, that is to say in definitive terms, the powerdelivered to the motor and its speed.

In the raising or winching-up direction represented by the arrows H forwinding up the cable, the supply pressure is applied to a hose 208 whichsupplies the motor through a non-return valve 209 shunted by a checkvalve 210, the function of which will be explained later. At the outletfrom the motor, the hydraulic fluid returns to the return R by a hose209 then via the servo-valve 205. A valve of the shuttle-valve type 211is fed simultaneously by the hoses 208 and 209 and allows the brake 105to be released both when pressure is applied to the hose 208 and when itis applied to the hose 209, thus releasing the motor both for theraising and for the descent, when this motor does actually receive asupply pressure.

For the descent, featured by the arrows D, the servo-valve 205 crossesover the paths of the hydraulic fluid. Thus, the pressure P is appliedto the hose 209 and the motor operates in reverse, allowing this descentto be controlled. This pressure is then also applied to the valve 210,which frees the passage of the fluid returning towards the hose 208 thentowards the reservoir 207. In this way, in the event of a malfunction ofthe brake 105 releasing the motor in the absence of raising or descentcontrol pressure, the delivery of the hydraulic fluid by the motortowards the hose 208 is blocked by the non-return valve 209 and thecheck valve 210, which very substantially stops this motor, give or takethe leakage, and therefore prevents the load from descending freelyunder its own weight.

in this device, during the descent, the hydraulic fluid passes twiceinto the servo-valve 205 and the operation of this motor is thus fullycontrolled by this servo-valve. Since the load tends to descendnaturally under the effect of its own weight, this control is excessive,which in particular increases the various hydraulic transients (shockwaves, resonance, cavitation . . . ) and may lead to jerky movements ofthe load during its descent.

Furthermore, the hydraulic control of the motor on the basis of thepressure leads on the one hand to a consumption of power which isprofitless as regards the helicopter for which this power is measured,and a heating-up, itself also profitless, of the oil in the hydrauliccircuit. Indeed, the energy resulting from the descent of the load isessentially dissipated at the motor by heating up the oil, and what ismore the drop in pressure of this oil between the supply and the returnis itself dissipated as heat, essentially by throttling at theservo-valve. By way of example, the descent of a load of some 250newtons at 5 m per second over a height of 750 m requires the use of 36litres of fluid per minute at a pressure of 200 bar, which correspondsto a power of 12 kW which has to be dissipated. Since the volume offluid available for such a purpose is some 20 l, the dissipation of thisenergy causes the temperature of these 20 l to rise by approximately 30°C. Such a temperature rise could perhaps be acceptable if taken inisolation, but the repetitive nature of these manoeuvres, frequentlynecessary under operating conditions, leads to a much greater totaltemperature rise which is the source of numerous drawbacks such asexcessive expansion of the hydraulic members, deterioration of the oil,and a release of heat into the helicopter which has to be dissipated bycooling systems.

SUMMARY OF THE INVENTION

In order to alleviate these drawbacks, the invention proposes a winchwith hydraulic motor especially for helicopter equipped with sonar, ofthe type comprising a reversible hydraulic motor for driving the winch,fed by a servo-valve as well as by a first supply hose and a secondsupply hose, mainly characterized in that this servo-valve is connectedto the motor by the first hose and that the second hose is connecteddirectly to the return circuit for the hydraulic fluid, the servo-valveallowing the first hose to be fed with hydraulic fluid under pressurefor winching-up, and allowing this first hose to be connected to thesecond hose to allow the hydraulic fluid to circulate in closed circuitwithout pressure for descent, during all of this descent.

According to another feature, the said servo-valve is a 4-wayservo-valve used essentially as a 3-way valve.

According to another feature, the winch further includes a third hoseconnecting the servo-valve to the second hose to allow the hydraulicmotor to be supplied, during the descent, with hydraulic fluid underpressure in just sufficient quantity to avoid the overheating of thefluid circulating in closed circuit.

According to another feature, the means by which the drum is driven bythe motor consist of gears having good efficiency both in the reversedirection and in the forward direction.

According to another feature, these drive means comprise a means oftransmission through an angle using a bevel gear followed by anepicyclic gear set.

According to another feature, the winch comprises means for furthermoresupplying the casing of the motor with hydraulic fluid under pressurewith sufficient flow rate to limit any possible additional overheating.

According to another feature, the winch comprises a back-up electricmotor connected to the hydraulic motor by a clutch controlled by a ramwhich engages this clutch under the effect of a lack of pressure.

According to another feature, this clutch also operates as a torquelimiter.

According to another feature, the winch further comprises a fourth hoseconnecting the first and second hoses by means of a relief valve whichallows the delivery pressure to be released when the winch starts torotate in the opposite direction during winching-up as a result of theload accidentally catching.

According to another feature, the winch further comprises a bypass valvewhich short-circuits the relief valve when the pressure of the hydraulicfluid starts to drop.

BRIEF DESCRIPTION OF THE INVENTION

Other specific features and advantages of the invention will emergeclearly in the following description given by way of non-limitingexample with reference to the appended figures which represent:

FIG. 1, a diagrammatic view of a known winch;

FIG. 2, a detailed diagram of the control members 104 of FIG. 1;

FIG. 3, a diagrammatic view of a winch according to the invention; and

FIG. 4, a detailed diagram of the control members 304 of FIG. 3.

DISCUSSION OF THE PREFERRED EMBODIMENTS

The diagram of a winch according to the invention represented in FIG. 3is simplified in the same way as the diagram of FIG. 1.

The hydraulic motor 101 drives the shaft 111 of the drum of the winchthis time via a means for transmission through an angle with bevel gear302 followed by an epicyclic gear set 312. This gearing system makes itpossible to obtain a much better efficiency in the reverse directionthan the worm system of the prior art, but other reduction-gear systemsgiving the same result could be used. It will be seen hereafter thatthis point is important in the invention.

The shaft of the hydraulic motor is moreover connected to a back-upelectric motor 107 by means of a clutch 309 and a reduction gear 108.This clutch is released by a ram 310 which operates under the hydraulicpressure from a hydraulic control unit 304. Thus, in the event of ahydraulic breakdown, the pressure disappears and the ram releases theclutch which engages and mechanically connects the electric motor to theshaft of the hydraulic motor. This operation takes place automaticallyin the event of a breakdown and there is thus no manual interventionrequired in this case.

The electric motor itself includes an electrically controlled brake 305operating on lack of current. The electric control thus consists insending current to the brake 305, which releases it, and to the motor107, which makes it turn.

Thus, when switching over to electrical operation, if the motor is notpowered the winch is automatically stopped in the position which it hasreached, without any possibility of it unwinding by itself.

Furthermore, it is observed that by comparison with the diagram of FIG.1, the stop control of the hydraulic unit from the control device 110used for engaging the electric motor with the shaft of the hydraulicmotor no longer exists, for the reasons which will be explained later.

The detailed diagram of the winch is represented in FIG. 4 using thesame conventions as FIG. 2.

The hydraulic motor 101 connected to the drum 203 supporting the load201 via the cable 202 is supplied from the source of hydraulic fluidunder pressure via a shut-off valve 204 piloted by a pilot electro-valve206 receiving a control signal C1.

This fluid under pressure is applied to the motor via a servo-valve 405of the same type as the 4-way servo-valve 205 but this time used as a3-way valve. This different use is achieved simply at the connections tothe valve.

In the direction of raising, featured by the arrows H, the hydraulicfluid passes through the servo-valve 405 via a hose 408 then returns tothe return in the reservoir 207 via a hose 409 which is this timeconnected up directly to this reservoir without passing through theservo-valve, hence the 3-way operation. This difference already makes itpossible to obtain a smaller drop in pressure head, and hence better useof the available energy.

The clutch control 310 receives the hydraulic pressure from the shut-offvalve 204 via a clutch electro-valve 401 controlled by an electricsignal C3. This electric signal C3 makes it possible to engage theelectric motor with the hydraulic motor as desired, even when pressureis established. By contrast, in the absence of pressure as has alreadybeen seen, clutch engagement is automatic.

For the descent of the load, featured by the arrows D, the servo-valve405 crosses over the hydraulic circuits under the control of theelectric signal C2. Under these conditions, the hydraulic fluid underpressure is applied to one outlet of the servo-valve which is pluggedfor the 3-way operation, apart from the alternative form describedlater. The hydraulic fluid leaving the motor 101, which turns whilebeing driven by the drum 203 under the tension on the cable 202, passesinto the servo-valve 405 and is looped back to the hose 409 via a returnhose 402. The sucking of the motor 101 prevents this fluid fromreturning to the reservoir 207 and causes it to travel in a direction Dback to motor 101 through hose 409. In this way, the hydraulic fluidcirculates in closed circuit in the circuit indicated by the arrows D,and since the mechanical drive system using bevel gear and epicyclicgear set has a good efficiency in reverse, a "natural" dynamicequilibrium becomes established which has the particular feature ofbeing stable and of not leading to the operating irregularitiesdescribed in the prior art.

Furthermore, the fluid which thus circulates in closed circuit issubject only to the pressure delivered by the motor which is used simplyto circulate this fluid. The power thus dissipated is therefore very lowand it is possible to avoid having to dissipate the power previouslydelivered by the source of high pressure as pure loss.

Finally, it is also possible to regulate the speed of descent bycontrolling a greater or lesser aperture of the servo-valve 405 by meansof the control circuit C2, this making it possible to throttle thehydraulic fluid to greater or lesser extents in its return circuit.

In the prior art, the speed at which the cable is unwound was inprinciple fixed by the speed of rotation of the drum fixed by the motorwhich operated under the effect of the applied oil pressure. Inprinciple, the control members were designed to fix a speed whichcorresponded to the natural descent of the sonar under the effect of itsown weight. In practice, there was nevertheless a risk that the drumwould start to turn too quickly and would unwind the cable too rapidly,thus leading to a risk of the turns detaching from the drum and becomingentangled which may lead to abrupt blockage of the assembly. Theinvention makes it possible to do away with this risk by obtaining anatural equilibrium without any constraint because it is the tension inthe cable which moves the drum by pulling. This means that the cablealways remains taut and can no longer become detached.

Furthermore, in contrast with the prior art, there is no longer any needto use a bypass system on the hydraulic circuit intended forshort-circuiting the motor in the event of a hydraulic breakdown and ofswitching to the electric motor for winching up the load. In fact, inthe prior art, since the servo-valve is closed in the event of ahydraulic breakdown, the motor can neither draw in nor deliver and thisinability to deliver leads to it becoming blocked unless of course thedelivery is short-circuited to the intake using a bypass. However, sucha bypass constitutes an additional component which can, moreover, itselfmalfunction and which has to be switched in positively in the event of amalfunction. Since in the invention there is no passage via theservo-valve on delivery, the motor is free to deliver all the fluid itcontains. It cannot, theoretically at least, and depending on the stateof the pressure in the various hydraulic circuits, draw in, but thiscircumstance does not cause it to become blocked because when it isempty it can nevertheless rotate, simply with very slight braking.Furthermore, it is observed that this same circumstance prevents thedrum and the motor from rotating in the opposite direction under theeffect of the load when this breakdown occurs during winching-up,because in this case the delivery will take place on the closed side ofthe servo-valve. This prevents the load from redescending of its ownaccord, without having to provide specific safety devices.

Nonetheless, another problem, that of heating, is encountered due to thefact that the amount of oil circulating is of a very small volume.Indeed, if we refer to the numerical example described earlier, thetension in the cable during the descent of the sonar into the water,which is substantially some 250 newtons for a speed of 5 m per second,corresponds to a power of some 1 kW. Assuming that the losses in thevarious mechanical drive members represent some 0.5 kW, there are still0.5 kW which have to be dissipated in the hydraulic circuit. The amountof energy to be dissipated is therefore much lower than that of theprior art. Nonetheless, since these 500 W would have to be dissipated inthe absence of other devices in an oil volume of substantially 50 cm³,the overheating would be difficult not to accept, even for a singlemanoeuvre.

In order to alleviate this drawback, the invention proposes to refreshthe oil, using a pipe 403 which is connected up between the outlet fromthe electro-valve which was said earlier theoretically to be plugged,but which is now therefore slightly open in order to feed this pipe, andthe hose 409 which allows the fluid to return to the motor when it isoperating as a pump during the descent. This feeding takes place ofcourse under the pressure P, and in order to avoid an excessive supplyof energy, the flow rate is limited preferably using a pipe of narrowcross-section or restriction featured in the figure as a flow restrictor404.

As a numerical example, it is possible to inject 2 l per minute underthe pressure of 200 bar supplied by the valve 204. Of course, the excessoil heated up in the motor is discharged to the return R. This oil ishot whereas the oil which comes to replace it is cold, and although thisadds an additional power of approximately 700 W, overheating is avoidedbecause the hot oil is taken back to the reservoir 207 from the returnR.

Furthermore, in practice servo-valves of this type operate not directlyunder the control of an electromagnet powered by the signal C2, but bymeans of a small intermediate hydraulic circuit known as "control flowrate" circuit represented in the figure by the loop 406 between the hose402 and the one which arrives from the valve 204. This loop consumes aflow rate of approximately 0.5 l of fluid which has to be taken intoaccount when assessing the additional oil injected, and under theseconditions the flow rate in the hose 403 is limited to substantially 1.5l.

The operations which have been described hitherto relate to the descentof the payload (the sonar) into the water, because this is the phasewhich lasts the longest, approximately 3 min. However, before enteringthe water the sonar covers the distance between the helicopter and thewater surface. This takes place very rapidly, a few seconds, because thedistance is short, approximately 20 metres, and because the load is thensome 800 newtons, namely 3 to 4 times greater than in the water. Becauseof the small volume of fluid used in the invention, the overheating thatoccurs during these few moments and which corresponds to the dissipationof an additional power of approximately 3 kW for a few seconds may betoo great. In order to avoid this effect, the invention proposes toincrease further the additional flow rate of oil in the motor by usingthis time a circuit which is already known elsewhere and which consistsin letting a flow rate of fluid into the casing of the motor by means ofa hose 410 fed by an electro-valve known as the heater valve 407. Thiscircuit is normally used to heat up the hydraulic circuit when it isvery cold, hence its name. According to the invention, uponinitialization of the descent from the helicopter, this electro-valvewill be actuated by a control signal C4 which will be stopped when it isdetected that the sonar is entering the water. This detection takesplace using known means because it is employed for other uses in theknown operation of the winch. By using an additional flow rate of 4 l offluid per minute in this way, it is thus possible to limit the increasein temperature of this fluid to 30° C., which is entirely satisfactory.The power dissipated during this short moment may reach 3 kW.

In order furthermore to solve the problem of excess tension in the cablewhen, during hydraulic winching-up, the load becomes caught up on thebottom or carried along and starts to pull on the cable because of therelative motion between the helicopter and the point at which the loadis caught, a load sensor which forms part of the known means of thewinch makes it possible to obtain a signal controlling the opening ofthe electric brake 305 and for releasing the clutch 309. The motor thenstarts to rotate in the opposite direction as a pump and delivers on thehose 408. In order to avoid the delivery pressure becoming greater thanthe inlet pressure, which could damage the hydraulic system, use is madeof a hose 411 which connects the hoses 408 and 409 via a relief valve412, set for example to 220 bar. This valve opens under the effect ofthe excess pressure and the fluid is returned to the return, whichcauses the pressure to drop and avoids damage, particularly to theservo-valve 405. This situation theoretically lasts only as long as isnecessary to open the servo-valve in order to release the pressure. Thisopening takes place after it has been detected that the load has becomecaught up, at system control logic level or, as last resort, manually.

When this same incident occurs during electric winching-up, use is madeof a bypass valve 413, set for example at 100 bar, which short-circuitsthe relief valve 412 and is controlled by a hose 414 connected to thepressure inlet on the hose between the valve 204 and the servo-valve405. As electric winching-up is used as a back-up measure because thereis no longer any hydraulic pressure, the absence of pressure in the hose414 causes the bypass valve 413 to open, which allows the motor todeliver on the return.

Finally, when there is a complete hydraulic and electrical breakdown, itis of course no longer possible to control anything. In theseconditions, the clutch is engaged and, to avoid any possibility ofdamage, the invention anticipates designing this clutch as a torquelimiter in order to make it slip, this allowing the cable to be paid outby braking at this clutch and by throttling of the fluid in the bypassvalve.

All of the control signals C1 to C4 will advantageously be obtainedusing a microprocessor which is suitably programmed and linked to thevarious sensors of the winch.

We claim:
 1. Winch with a hydraulic system, comprising:a reversiblehydraulic motor driving a winch cable for raising and lowering a loadconnected to the winch cable; a source of hydraulic fluid at an elevatedpressure; a first supply hose connected to said motor for driving themotor in a direction to raise the load when hydraulic fluid from saidsource is supplied to said motor via said first supply hose; aservovalve connected to said first supply hose and to said source forselectively connecting said first supply hose to said source to supplyhydraulic fluid to said motor for raising the load; a second supply hosedirectly connecting said motor to a low pressure hydraulic fluid return;and a return hose connecting said servovalve to said second supply hose,wherein said servovalve is movable to a position connecting said firstsupply hose to said return hose so that hydraulic fluid can circulate ina closed circuit substantially without pressure during a descent of theload.
 2. Winch according to claims 1, including means not including saidservo value for supplying the motor with hydraulic fluid under pressure.3. The winch of claim 1 wherein said servovalve is a four way servovalvehaving a substantially plugged port so as to function as a three wayservovalve.
 4. Winch according to claims 3 characterized in that itfurther includes a third hose connecting the servo-valve to the secondhose to allow the hydraulic motor to be supplied, during the descent,with hydraulic fluid under pressure in just sufficient quantity to avoidthe overheating of the fluid circulating in closed circuit.
 5. The winchof claim 4 including means connecting said motor to the winch cable,said connecting means including a gear train having substantially thesame efficiency when rotating in two directions.
 6. The winch of claim 5wherein said gear train includes a bevel gear and an epicyclic gear set.7. Winch according to claim 4 including a back-up electric motorconnected to the hydraulic motor by a clutch controlled by a ram whichengages said clutch in response to a lack of hydraulic pressure. 8.Winch according to claim 7, wherein said clutch also acts as a torquelimiter.
 9. Winch according to any claim 4, characterized in that itfurther comprises a fourth hose connecting the first and second hoses,by means of a relief valve.
 10. Winch according to claim 9, furthercomprising a bypass valve which short-circuits the relief valve when thepressure of the hydraulic fluid starts to drop.